High-speed data communication integrated circuit (IC) dies are known to include both drivers and receivers. The driver of one such IC connects to the receiver of another via one or more signal transmission lines. Both the driver and receiver circuits include termination elements that attempt to match the characteristic impedance of the transmission line to the output impedance of the driver and input impedance of the receiver, as impedance mismatches degrade signal quality and consequently reduce communication speed and reliability.
Some conventional communication systems employ control systems that calibrate the impedance of on-die termination (ODT) elements for improved impedance matching. These systems work well in many applications. Still, high-speed data communication circuits must achieve ever greater performance levels, at competitive prices, to satisfy customer demand. Furthermore, different customers typically have different requirements that may not be met by a given ODT configuration. One customer might favor power efficiency over speed, or may prefer different termination voltages or impedances. There is therefore a need for ODT circuits that offer customers access to a broader range of termination topologies and values. Further, each supported topology or value should be capable of precise calibration to account for process variations. Such calibration might be repeated as needed to compensate for changes due to supply-voltage and temperature fluctuations.